Knot security: how many throws does it really take?

Full article available online at Healio.com/Orthopedics. Search: 20120327-16 The purpose of this study was to determine the minimum number of throws needed for knot security for square knots using 5 common suture materials and 3 common sizes by in vitro single load to failure biomechanical testing. The hypothesis was that each suture combination studied would share a common minimum of at least 5 throws to guarantee security. Five suture materials (FiberWire [Arthrex, Inc, Naples, Florida], Monosof, Surgipro, Maxon, and Polysorb [Covidien, Mansfield, Massachusetts]) with varying suture sizes (#5, #2, 0, 2-0, and 4-0) were tied in vitro, varying the number of square knot throws (3, 4, 5, and 6). Twenty knots for each combination were statically loaded to failure in tension; whether the knot failed by fracture or slippage and the tensile strength at knot failure was determined. For the tested materials, at least 5 flat square throws should be used to confer knot security based on a binomial proportion score 95% confidence interval (CI) 0.84 to 1.0 or at least 4 throws for a 95% CI of 0.76 to 0.99. FiberWire requires 6 flat square throws per knot for security at either 95% CI level. Unless a surgeon has specific knowledge of experimental evidence that fewer throws are necessary for a specific application, the default should be a minimum of 4 throws, with 5 conferring additional security in most situations, and FiberWire requiring 6 throws. Drs Tidwell and Prud’homme and Mr Kish are from the Department of Orthopaedics, West Virginia University, Morgantown, West Virginia; and Dr Samora is from the Department of Orthopaedics, The Ohio State University, Columbus, Ohio. Drs Tidwell, Samora, and Prud’homme and Mr Kish have no relevant financial relationships to disclose. This study received no external funding. The FiberWire suture was donated by Arthrex, Inc, Naples, Florida. The authors thank Suzanne Smith for her editing help. Correspondence should be addressed to: John E. Tidwell, MD, Department of Orthopaedics, West Virginia University, PO Box 9196, Morgantown, WV 26506-9196 (jtidwell@hsc.wvu.edu). doi: 10.3928/01477447-20120327-16 Knot Security: How Many Throws Does It Really Take? John E. TidwEll, Md; VincEnT l. Kish, As; JuliE B. sAMorA, Md, Phd; JosEPh Prud’hoMME, Md Figure: A flat square knot with 2 single-turn throws.